1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to a method of shingled printing with a color ink jet printer.
2. Description of the Related Art.
Ink jet printers commonly include a printhead which is mounted on a carriage assembly. The carriage assembly is movable in a transverse direction, relative to an advance direction of a print medium such as paper. As the printhead is moved across the print medium during a particular pass of the carriage assembly, ink is selectively jetted from ink jetting orifices formed in the printhead and is deposited on the print medium at corresponding ink dot placement locations in the image area of the print medium. Since the printhead moves in a direction transverse (e.g., perpendicular) to the advance direction of the print medium, each ink jetting orifice passes in a linear manner over the print medium. The line associated with each ink jetting orifice which overlies the print medium is commonly referred to as a raster or raster line. A plurality of rasters which extend across the image area of the print medium are disposed vertically adjacent to each other in the advance direction of the print medium.
Multi-color ink jet printers typically include a printhead having a plurality of ink jetting orifices therein. The ink jetting orifices are segregated into different arrays of ink jetting orifices, with each array corresponding to the different color inks which are to be jetted onto the print medium. With a known tri-color printhead, a first array of ink jetting orifices is used for jetting yellow ink onto the print medium, a second array of ink jetting orifices is used for jetting magenta ink onto the print medium, and a third array of ink jetting orifices is used for jetting cyan ink onto the print medium. The first, second and third arrays of ink jetting orifices are sequentially arranged relative to the advance direction of the print medium. Associated with each ink jetting orifice in the three arrays of ink jetting orifices is a corresponding ink jetting heater. Actuation of a particular ink jetting heater causes the formation of a bubble within the ink disposed adjacent thereto and expels the ink from the associated ink jetting orifice. A host computer connected with the printer transmits raster information to the printer for selective actuation of the ink jetting heaters.
To render a full color image, the tri-color printhead is passed across a print medium such as paper in a horizontal direction perpendicular to the vertical direction of alignment of the orifices in the printhead. Between passes of the printhead, the print medium is moved in the advance direction. For a raster, or row of printed dots, which contains at least one of each of cyan, magenta and yellow dots, the color printhead must be passed at least three times, once passing to deposit any cyan dots present in the given raster, once passing to deposit any magenta dots, and once passing to deposit any yellow dots. Of course, for any pass of the color head all 48 color orifices can be used, depositing the cyan, magenta, and yellow inks at different raster locations. The most time efficient technique for depositing ink therefore causes the tri-color printhead to pass across each raster of the page at most three times.
With a conventional method of printing with a tri-color ink jet printer as described above, objectionable print artifacts may occur because of the sequencing and/or timing between the placement of the different color ink dots on the print medium. For example, print artifacts such as horizontal color/black banding or intercolor bleeding may occur.
One known solution to the problem of a color/black banding artifact is known as shingling or interlaced printing. For a 50% shingling mode (i.e., 2-pass or 50% interlace level), approximately 50% of the dots are placed on any given pass of the printhead. The candidate dots are selected according to a checkerboard pattern. The remaining 50% of the dots are placed on a subsequent pass of the printhead. For a raster which contains cyan, magenta, yellow, and black dots, the color printhead must be passed at least six times with a 50% shingling mode, twice depositing any cyan dots present in the given raster, twice depositing any magenta dots, and twice depositing any yellow dots.
When printing with an ink jet printer using a shingling method as described above, it is known to assign a particular interlace level to the tri-color printhead for use during printing on the print medium. For example, assuming that an image area corresponds to 16 rasters, it is known to assign a single interlace level for each of the cyan array of ink jetting orifices, magenta array of ink jetting orifices and yellow array of ink jetting orifices. It is also known to change the interlace level between portions of the image area which are spaced apart in the advanced direction of the print medium. Finally, when using an ink jet printer having both a tri-color printhead and a black printhead, it is known to print using one interlace level for the tri-color printhead and a different or no interlace level for the black printhead.
A selected one of a plurality of interlace levels may be used to effectively reduce a print artifact in a particular portion of an image area. For example, a 50% shingling technique (2 pass shingling) may be used to reduce a print artifact in one portion of the image area, while a 33% shingling technique (3 pass shingling) may be used to reduce a print artifact in a different part of the image area. Conventional methods of shingling would thus select the more restrictive 33% interlace level (3 pass shingling) for both portions of the image area so that all print artifacts are reduced. This may not be optimum from an efficiency stand point in terms of throughput of the printer.
What is needed in the art is a method of printing using a shingling technique which is more adaptable to using different interlace levels for different parts of the image area, while at the same time maximizing the throughput rate of the printer.